Method of preserving the shape of steel springs in the process of tempering



UNITED STATES PATENT OFFICE.

DAVID M. SMITH, OF SPRINGFIELD, VERMONT.-

METHOD OF PRESERVING THE SHAPE OF STEEL SPRINGS IN THE PROCESS OF TEMPERlNG.

Specification forming part of Letters Patent No. 5,979, dated December19, 1848.

To all whom it may concern:

Be it known that I, DAVID M.'SMITH, of

Springfield, in the cou nty of Windsor and State of Vermont, haveinvented a new and useful process of restoring the shape of flat hardcurved steel sprin gs which have become warped or twisted out of shapeduring the operation of tempering the same; and I do hereby declare thatmy invention is fully described and represented in the followingspecification.

It is a fact wellknown to persons experienced in tempering steel springs(made of steel strips or hands of steel) that they often warp or bendout of shape during the tempering process, and that after such occurs itis very clifficu lt to restore them to their original or proper shape.The method which I adopt for restoring such a spring after it has beenhardened and its temper drawn in the 'usual way consist'sin confining itupon and to a metallic or other suitable pattern or mold of the shapewhich it is desirable the spring shall receive, and plunging the patternand spring confined upon it into molten lead or some metallic or mineralsubstitute in a state of fusion or in a fluid state, and heated to ahigh and proper temperature. For example, suppose it is desirable torestore a truss-spring or abdominal-supporter hipspring to the shapewhich it should have previous to being applied to the body. Such aspring is generally made out of a thin strip of steel, bent so as tospring and fit closelyaround the loins or that part of the bodyimmediately above one of the hips. I prepare an iron pattern or moldwith an external surface of a shape to correspond with that I desire togive to theinternal surface of the strip of steel which is to be placedupon it; This being done, I lay the said steel strip upon said surface,and bend it and make it fit down closely upon the said surface, and bymeans of any suitable clamps or contrivances I confine the strip, at itsend or elsewhere, as the case may require, down upon said surface. I donot consider it necessary that a metallic pattern or shape should alwaysbe used, as said pattern or shape may be made of any suitable materialcapable of withstanding a high degree of heat, or that,

degree of heat to which it may be subjected. The pattern and articleaffixed upon it is next to be plunged into a mass or bath of melted leador other proper metal or combination of metals in a fused or meltedstate, and there dipping it into a cold-water bath.

Such process, however, I consider to differ essentially from my mode ofhardening and temperin g a spring and restoring or preserving its shapeafter it has been tempered. Springs such as are used in trusses orabdominal supporters-that is, hip or body springs-and which are made ofthin and flat bands or strips of steel, cannot be hardened on a moldwithout serious danger of being broken during the process. \Vhen suchsprings are attempted to be so hardened they will break in a majority ofcases, the cause of their breaking being in consequence of the waterinto which they are plunged having access to but one side of them,

as it were. That side of the spring which is bound closely in contactwith the mold is not cooled so fast as the opposite side, for fromvarious'causes the water cannot get access to it as quickly as it doesto the opposite side. It is a well-known fact that the external surfaceof a heated piece of metal is that part of it which is cooled firstduring the process of hardening or When a flat spring is bound closeagainst amold its external surface will cool quicker than the internalsurface of it, or that which is in contact with the mold, for the heatof the mold itself is one cause which prevents the inner surface of thespring from cooling so quickly as the outer surface thereof. The unequalreduction of temperature of the surfaces of the spring is the cause, orone prominent cause, of rupture. Thus it will be seen that, althoughsome kinds of springs (particularly those made of round steel) can behardened on a mold, there are others-viz., those made of flat and thinsteelwhich cannot be so hardened without great danger of being brokenduring the process.

In making a spring of aflat band or strip of steel I bring it to aboutthe shape required, and next harden it in the usual way and not on amold. 1 next draw the temper to the extent required to enable me to bendit, and applyit to the mold withoutdanger of breaking it whileapplyingit and clamping it to the mold.- This beingaccomplished,Iafterward plunge the mold and spring into the bath of metal, ashe'reinbefore described, and by so doingI preserve the shape of thespring which was given to it by the mold. It must be borne in mind that,although Icould bend the spring so as to make it fit to the mold, yetthe elasticity of the spring would or might, if the spring was removedfrom the mold before being dipped in the bath, cause it to take asomewhat different shape. The dipping the mold and spring together intothe bath preserves the shape of the latter. Therefore I wish itunderstood that I lay no claim to the process of hardening a spring on amold and drawing the temper while on the mold; but

That which I do claim, and as particularly applicable to the manufactureof curved flat springs for trusses or various other articles, is

The improved process above detailed or described, the same consisting,first, in hardening the spring in the usual manner when off the mold;second, in drawing the temper (it being still oft the mold) to suchextent as to enable me to apply it to the mold without danger ofbreaking it whileso doing; third, in clamping said spring to a mold andplunging it and the mold so clamped together into a bath of melted leador other suitable metal or metals or material or materials in a fluidstate, and raised to the temperature necessary to produce the desiredeffect of preserving the shape of the spring or that given to it by themold.

In testimony whereof I have hereto set my signatnrethis 29th dayofNovember, A. D. l 848.

DAVID M. SMITH.

Witnesses:

R. H. EDDY, JACOB EDSON.

